DESCRIPTION: The long range goal of this project is to develop and use the technology of functional magnetic resonance imaging (FMRI) to elucidate the brain mechanisms responsible for normal vision and for brain-related visual pathologies. to this end, there are several specific aims. A compute model of the functional topography of human visual cortex will be developed and combined with a surface model of cerebral cortex anatomy taken from a widely accepted human brain atlas. Together with improved measurements of human retinotopic organization, the model will be used to test the hypothesis that retinotopic organization and visual area topography are functionally equivalent in humans and monkeys. FMRI will also be used to observe brain activity as subjects perform a vision task designed to identify visual areas associated with sequential stages of visual shape processing. These experiments will be combined with tests of color vision to differentiate areas in ventral occipital and temporal cortex on the basis of their functions as well as their retinotopic organization. Another way that human visual areas can differ is in the relative influence of task factors such as visual processing load and attention. By using a test in which processing load is manipulated, we will test the hypothesis that traditional visual areas are load sensitive but that other task-related areas are not, thus suggesting an important new basis for functionally differentiating cortical areas. Additional tests will be used to quantitatively asses the role of spatial and featural attention in modulating the responses of difference human visual areas. These tests will establish if both types of attention are equally effective, how they interact, and whether there is a gradient of effect across areas at successively higher stages of processing. Together the tests of topographic organization, functional selectivity and task factor control will provide converging evidence for the functional specialization of visual cortex. This information will then be used to account for specific visual deficits in a select group of patients with visual system pathology. A few such patients will be studied comprehensively to provide a more detailed explanation of their deficits that has previously been possible. The results of these experiments, obtained through direct measurement of human brain activity, will significantly advance our understanding of visual system organization and of brain function in general. The project will further develop and test the capabilities of FMRI as a research and diagnostic tool and in so doing will expand its potential as a powerful new paradigm for exploring the human brain.